CARBON STABLE ISOTOPIC COMPOSITION OF BENTHIC FORAMINIFERS FROM THE NORTH OF THE SOUTH CHINA SEA: INDICATOR OF METHANE-RICH ENVIRONMENT

Carbon stable isotopic composition of benthic foraminifers in piston cores and surface sediments from the north of the South China Sea have been studied. The carbon stable isotope analyses of infaunal species (Uvigerina spp.) revealed a distinction between seep and non-seep foraminifera.Uvigerina spp.collected from Dongsha area (seep environment) exhibited highly variable and strongly depleted δ¹³C values,ranging from -0.52‰ to -5.68‰ and the mean values -1.41‰; The Uvigerina spp. δ¹³C values ranged from -0.36‰ to -1.10‰, mean -0.75‰ in Shenhu area(non-seep environment); and δ¹³C values ranged from -0.01 to -0.89‰, mean -0.45‰ in Xisha Trough (non-seep environment). The relations between δ¹³C values,organic carbon (TOC) and methane (CH₄) content showed that carbon isotopic ratios had a negative excursion trend with methane conent increasing. Negative carbon isotopic excursion of Uvigerina spp. mostly occurred during LGM, when dissolved inorganic carbon of bottom water and δ¹³C of core sediments were negative excursions. The studies imply that the carbon isotopic excursion may be used to indicate methane-rich environment.